your car is under warranty, if you do not wish to get into a huge legal issue if a problem arrises i'd suggest you stick with genuine toyota motor oil for now and once the warranty runs out THEN use better oils
toyota oil is not good value for money but if you wish to hold on to your warranty i'd suggest you stick with it for now. no need for a flush or anything else, just open the drain nut, change the filter and refil the oil. when you "upgrade" to a better oil (afger warrnty expires) then go for an engine flush, your engine will need it by then. i'd suggest the liquimoly engine flush as it is quite good and i have used it myself.